1. Text: Historical Geology
Evolution of Earth and Life Through Time
4th edition
by Wicander and Monroe

2. The Dynamic and Evolving Earth
Chapter 1
The Dynamic and Evolving Earth

3. The Movie of Earth’s History
What kind of movie would we see
if it were possible to travel back in time
and film Earth’s History
from its beginning 4.6 billion years ago?
It would certainly be a story of epic proportions
with great special effect
and a cast of trillions
twists and turns in its plot
with an unknown ending
Although we cannot travel back in time,
the Earth’s History is still preserved
in the geologic record

4. Subplot: Landscape History
In this movie we would see
a planet undergoing remarkable change as
continents moved about
ocean basins opened
mountain ranges grew along continental margins
and where continents collided
The oceans and atmosphere would
form and grow
change circulation patterns
cause massive ice sheets to form and grow
and then melt away
Extensive swamps or vast interior deserts
would sweep across the landscape

5. Subplot: Life’s History
We would also witness
the first living cells evolving
from a primordial organic soup
between 4.6 and 3.6 billion years ago
Cell nuclei would evolve,
then multicelled soft-bodied animals
followed by animals with skeletons and then backbones
The barren landscape would come to life as
plants and animals moved from their watery home
insects, amphibians, reptiles, birds and mammals
would eventually evolve

6. Earth is a Dynamic and Evolving Planet
Changes in its surface
Changes in life
Images from left to right:
Changes in its surface
Artist’s rendition of how Earth is thought to have appeared about 4.6 billion years ago.
Paleogeography of the world for the Late Cambrian Period.
Apollo 17 view of Earth. Africa, Arabian Peninsula, Madagascar, Antarctica, South Atlantic Ocean , Indian Ocean.
Changes in life
Possible precursor of life: bacterium-like proteinoid.
Reconstruction of Middle Devonian reef from the Great Lakes area Shown are corals, ammonoids, trilobites and brachiopods.
Cretaceous Pteranodon.

7. At the End of the Movie The movie’s final image is of Earth,
a shimmering blue-green oasis
in the black void of space
and a voice says,
“To be continued.”

8. The Movie’s Theme Every good movie has a theme,
and “The History of Earth” is no exception
Three interrelated themes run throughout it
The first is that Earth’s outermost part
is composed of a series of moving plates
Plate tectonics
whose interactions have affected its physical and biological history
The second is that Earth’s biota
has evolved or changed throughout its history
organic evolution

9. Earth is a System of Interconnected Subsystems
Atmosphere (air and gases)
Hydrosphere (water and oceans)
Biosphere (plants and animals)
Lithosphere (Earth’s rocky surface)
Interior (mantle and core)

10. Interactions in Earth’s Subsystems
Atmosphere
Biosphere
Gases from respiration
Transport of seeds and spores

11. Interactions in Earth’s Subsystems
Wind erosion, transport of water vapor for precipitation
Mountains divert air movements
Atmosphere
Lithosphere

12. Interactions in Earth’s Subsystems
Source of sediment and dissolved material
Water and glacial erosion, solution of minerals
Hydrosphere
Lithosphere

13. This class is about historical geology What is Geology?
From the Greek
geo (Earth) logos (reason)
Geology is the study of Earth
Physical geology studies Earth materials,
such as minerals and rocks
as well as the processes operating within
and on Earth’s surface

14. Historical Geology In historical geology we study
changes in our dynamic planet
how and why past events happened
implication for today’s global ecosystems
Principles of historical geology
not only aid in interpreting Earth’s history
but also have practical applications
William Smith, an English surveyor/engineer
used study of rock sequences
to help predict the difficulty of excavation
in constructing canals

15. Scientific Method The scientific method
an orderly and logical approach
Gather and analyze facts or data
A hypothesis is a tentative explanation
to explain observed phenomena
Scientists make predictions using hypotheses
then they test the predictions
After repeated tests,
if one hypothesis continues
to explain the phenomena,
scientists propose it as a theory

16. Formulation of Theories
Theory
colloquial usage - speculation or conjecture
scientific usage
coherent explanation for one or several related natural phenomena
supported by a large body of objective evidence

17. Origin of the Universe The Big Bang occurred 15 billion years ago
and is a model for the beginning of the universe

18. Evidence for the Big Bang
Universe is expanding
How do we determine the age?
measure the rate of expansion
backtrack to a time when the galaxies
were all together at a single point
Pervasive background radiation of 2.7º above absolute zero
is the afterglow of the Big Bang

19. Big Bang Model Initial state: During 1st second:
No time, matter or space existed
There is no “before the Big Bang”
Universe consisted of pure energy
During 1st second:
Very dense matter came into existence
The four basic forces separated
gravity, electromagnetic force, 2 nuclear forces
Enormous expansion occurred

20. Big Bang Model (cont.) 300,000 years later:
atoms of hydrogen and helium formed
light (photons) burst forth for the first time
During the next 200 million years:
Continued expansion and cooling
Stars and galaxies began to form
Elements heavier than hydrogen and helium
began to form within stars by nuclear fusion

21. Features of Our Solar System
In a spiral arm of the Milky Way Galaxy
Sun
9 planets
101 known moons (satellites)
a tremendous number of asteroids
most orbit the Sun between the orbits of Mars and Jupiter
millions of comets and meteorites
interplanetary dust and gases

22. Relative Sizes of the Sun and Planets

23. Solar System Configuration

24. Origin of Our Solar System
Solar nebula theory
cloud of gases and dust
formed a rotating disk
condensed and collapsed due to gravity
forming solar nebula
with an embryonic Sun
surrounded by a rotating cloud

25. Embryonic Sun and Rotating Cloud
Planetesimals have formed
in the inner solar system,
and large eddies of gas and dust
remain far from the protosun

26. The Planets Terrestrial Planets
Mercury
Venus
Earth
Mars
small, composed of rock, with metal cores
Jovian Planets
Jupiter
Saturn
Uranus
Neptune
large, composed of hydrogen, helium, ammonia, methane, relatively small rocky cores

27. Earth’s Very Early History
Started out cool about 4.6 billion years ago
probably with uniform composition/density
Mostly:
silicate compounds
iron and magnesium oxides
Temperature increased. Heat sources:
meteorite impacts
gravitational compression
radioactive decay
Heated up enough to melt iron and nickel

28. Earth’s Differentiation
Differentiation = segregated into layers of differing composition and density
Early Earth was probably uniform
Molten iron and nickel sank to form the core
Lighter silicates flowed up to form mantle and crust

29. Forming the Earth-Moon System
Impact by Mars-sized or larger planetesimal with young Earth
4.6 to 4.4 billion years ago
ejected large quantity of hot material,
and formed the Moon

30. Forming the Earth-Moon System
Most of the lunar material
came from the mantle of the colliding planetesimal
The material cooled
and crystallized
into lunar layers

31. Forming the Earth-Moon System
Most of the lunar material
came from the mantle of the colliding planetesimal
The material cooled
and crystallized
into lunar layers

32. Moon Light-colored areas are lunar highlands Provide striking evidence
Heavily cratered
Provide striking evidence
of massive meteorite bombardment

33. Earth—Dynamic Planet Earth was also subjected
to the same meteorite barrage
that pock-marked the Moon
Why isn’t Earth’s surface also densely cratered?
Because Earth is a dynamic and evolving planet
Craters have long since been worn away

34. Earth’s Interior Layers
Crust km thick
continental and oceanic
Mantle
composed largely of peridotite
dark, dense igneous rock
rich in iron and magnesium
Core
iron and a small amount of nickel

35. Earth’s Interior Layers
Lithosphere
solid upper mantle and crust
Crust km thick
continental and oceanic
Mantle
composed largely of peridotite
dark, dense igneous rock
rich in iron and magnesium
Asthenosphere
part of upper mantle
behaves plastically and slowly flows
Core
iron and a small amount of nickel

36. Earth’s Interior Layers
Lithosphere
solid upper mantle and crust
broken into plates that move over the asthenosphere
Asthenosphere
part of upper mantle
behaves plastically and slowly flows

37. Earth’s Crust outermost layer continental (20-90 km thick)
density 2.7 g/cm3
contains Si, Al
oceanic (5-10 km thick)
density 3.0 g/cm3
composed of basalt

38. Plate Tectonic Theory
Lithosphere is broken into individual pieces called plates
Plates move over the asthenosphere
as a result of underlying convection cells

39. Modern Plate Map

40. Plate Tectonic Theory At plate boundaries Movement at plate boundaries
Volcanic activity occurs
Earthquakes occur
Movement at plate boundaries
plates diverge
plates converge
plates slide sideways past each other

41. Plate Tectonic Theory Types of plate boundaries
Divergent plate boundary
Mid-oceanic ridge
Continental-continental convergent plate boundary
Continental-oceanic convergent plate boundary
Oceanic-oceanic convergent plate boundary
Trench
Transform plate boundary

42. Plate Tectonic Theory Influence on geological sciences:
Revolutionary concept
major milestone
comparable to Darwin’s theory of evolution in biology
Provides a framework for
interpreting many aspects of Earth on a global scale
relating many seemingly unrelated phenomena
interpreting Earth history

43. Plate Tectonics and Earth Systems
Plate tectonics is driven by convection
in the mantle
and in turn drives mountain building
and associated igneous and metamorphic activity
Solid Earth
Arrangement of continents affects
solar heating and cooling,
and thus winds and weather systems
Rapid plate spreading and hot-spot activity
may release volcanic carbon dioxide
and affect global climate
Atmosphere

44. Plate Tectonics and Earth Systems
Continental arrangement affects ocean currents
Rate of spreading affects volume
of mid-oceanic ridges and hence sea level
Placement of continents may contribute
to the onset of ice ages
Hydrosphere
Movement of continents creates corridors
or barriers to migration,
the creation of ecological niches,
and transport of habitats into
more or less favorable climates
Biosphere

45. Theory of Organic Evolution
Provides a framework
for understanding the history of life
Darwin’s
On the Origin of Species by Means of Natural Selection, published in 1859,
revolutionized biology

46. Central Thesis of Evolution
All present-day organisms
are related
and descended from organisms
that lived during the past
Natural selection is the mechanism
that accounts for evolution
Natural selection results in the survival
to reproductive age of those organisms
best adapted to their environment

47. History of Life The fossil record provides perhaps
the most compelling evidence
in favor of evolution
Fossils are the remains or traces
of once-living organisms
Fossils demonstrate that Earth
has a history of life

48. Geologic Time From the human perspective time units are in
seconds, hours, days, years
Ancient human history
hundreds or even thousands of years
Geologic history
millions, hundreds of millions, billions of years

49. Geologic Time Scale
Resulted from the work of many 19th century geologists who
pieced together information
from numerous rock exposures,
constructed a sequential chronology
based on changes in Earth’s biota through time
The time scale was subsequently dated in years
using radiometric dating techniques

50. Geologic Time Scale

51. Uniformitarianism Uniformitarianism is a cornerstone of geology
is based on the premise that present-day processes
have operated throughout geologic time
The physical and chemical laws of nature
have remained the same through time
To interpret geologic events
from evidence preserved in rocks
we must first understand present-day processes
and their results
Rates and intensities of geologic processes
may have changed with time

52. How Does the Study of Historical Geology Benefit Us?
Survival of the human species
depends on understanding
how Earth’s various subsystems
work and interact
Study what has happened in the past,
on a global scale,
to try and determine how our actions
might affect the balance of subsystems in the future

53. We “Live” Geology Our standard of living depends directly on
our consumption of natural resources
resources that formed millions and billions of years ago
How we consume natural resources
and interact with the environment determines
our ability to pass on this standard of living
to the next generation

54. Summary Earth is a system Geology is the study of Earth
of interconnected subsystems
Geology is the study of Earth
Historical geology is the study
of the origin and evolution of Earth
Scientific method is
an orderly, logical approach
to explain phenomena,
using data,
formulating and testing hypotheses and theories
Universe began with
a big bang 15 billion years ago

55. Summary Solar system formed 4.6 billion years ago
by condensation and gravitational collapse
of a rotating interstellar cloud
Earth formed 4.6 billion years ago
as a swirling eddy in the solar system nebula
Moon may have formed
when a planetesimal collided with Earth
4.6 to 4.4 billion years ago
Earth probably started solid
then differentiated into layers
as it heated and melted

56. Summary Earth’s layers mostly solidified
into the core, mantle and crust,
with the upper mantle and crust
making up the soft asthenosphere
and the solid lithosphere
Lithosphere is broken into plates
that diverge, converge and
slide sideways past each other
Plate tectonics is a unifying theory
that helps explain features and events
including volcanic eruptions,
earthquakes and mountain forming

57. Summary Central thesis of organic evolution is An appreciation
that all living organisms evolved
from organisms that existed in the past
An appreciation
of the immensity of geologic time
is central to understanding Earth’s evolution
Uniformitarianism holds that the laws
of nature have been constant through time
Geology is part of our lives
and our standard of living depends
on our use of natural resources
that formed over billions of years